1. Field of the Invention
This invention relates to a copper alloy material and, in particular, to a copper alloy material that is excellent in mechanical strength such as tensile strength and yield strength, in elongation, in electric conductivity, in bending workability, and in bonding reliability in the case of using a Pb-free solder. This invention also relates to a method of making the copper alloy material.
2. Description of the Related Art
In recent years, an electronic hardware such as a cellular phone or notebook PC is downsized, low-profiled and reduced in weight. Along with this, electric and/or electronic components used therein tend to be reduced in weight, length and thickness.
In the downsizing, although materials used therein also have to be reduced in thickness, a material is needed to have a high mechanical strength (herein also called simply “strength”) even when it has the reduced thickness so as to keep a reliability in properties. Further, in order not to arise any crack in the bending process of parts, it also needs to have a good elongation. It is not suitable that the material has a difference in properties (anisotropy) between in a rolling direction and in an orthogonal direction to the rolling direction thereof, and it is important that the material has good properties in any directions.
Further, generated Joule heat increases with increasing in applied current and in the number of electrodes due to the sophistication of equipment. Thus, the material also needs to have a good electric conductivity as well as the mechanical strength. Such high electric conductivity is needed especially in a terminal and connector material for automobiles and a lead frame material for power IC, where applied current goes on increasing rapidly.
On the other hand, solder bonding is generally used for connecting and mounting the above electric and electronic parts. Although Sn—Pb eutectic system solders have been mainly used conventionally, Pb-free solders with a high Sn concentration are recently in wide use since Pb is restricted as a harmful material.
Due to the change from the Sn—Pb eutectic system solders used conventionally to the Pb-free solders, the following problems occur which have never happened before. Since most of the Pb-free solders have a higher melting point than the conventional Sn—Pb eutectic system solders, heating temperature in bonding the parts is needed to be higher than conventional one when the Pb-free solder is applied. When the heating is repeated in the process of assembling the electric and electronic parts, the interdiffusion between the Cu in the parts and the Sn in the solder is promoted at the bonding interface which is subjected to high temperature. As a result, the formation and growth of Cu—Sn intermetallic compounds at the bonding interface is promoted than before. The intermetallic compounds formed (or generated) are mainly Cu6Sn5 and Cu3Sn. Since especially Cu3Sn is a brittle material, the bonding reliability will be degraded according as its growth progresses at the bonding interface.
Various copper alloys are used as materials for the electric and electronic parts. Especially copper alloys containing Cu—Ni—Si as a main component are suggested as a material to have a high mechanical strength and a high electric conductivity (e.g., JP-A-2002-266042, and JP-B-2572042, 2977845 and 3465541).
However, the Ni contained in the copper alloys has a high diffusion rate toward the solder layer and can promote the formation and growth of the intermetallic compound between the Cu and the Sn. Therefore, the intermetallic compound will be grown easily when the content of Ni increases in the above Cu—Ni—Si alloys.
Further, in the Cu—Ni—Si alloys, if it is intended to have a high strength, the bending workability deteriorates and the an isotropy in mechanical properties becomes significant. Thus, it is difficult to satisfy simultaneously these properties in the Cu—Ni—Si alloys.